The present invention relates to an apparatus for the detection of splits in logs and other wooden members, and specifically to an apparatus employing ultrasonic energy to detect and characterize such splits. The wooden members may be trees, logs, beams, planks, lumber, boards or wood composites and the like.
When logs are sawn to size in the field using commercial harvesters, they are often subject to the creation of splits when cut. This is because one end of the log is unsupported during the cutting operation. Splits also occur when the tree is initially felled. The splits are undesirable, introduce defects in the lumber that is sawn from the logs, and thereby reduce the value of the log itself. A recent examination of the problem indicates that up to 70% of logs harvested in this manner contain splits. If the problem is detected in the field at the time of sawing, then either the operator can modify his/her practice to reduce this incidence, or the logs can be cut longer such that sufficient material will remain free of defects. In other words, if a 12 foot long clear log is desired, and the harvester detects end splits for a distance of 12 inches, then the next cut will be made so as to have the required 12 feet after the defective portion is removed.
Traditionally identification of defects and other features affecting lumber grade has been performed visually, for example, by a saw operator visually inspecting the log or board prior to determining the necessary cross or rip cuts that will yield the best product output or yield. Recently a number of electronic scanning systems have been produced using cameras and lasers to automate this visual process. Such optical techniques are limited to the detection of superficial defects in the wooden members and even these techniques may be defeated by dirt, bark, stain or other markings on the outside of the log. More importantly, internal defects such as splits are generally not visible.
What is needed is an apparatus for detecting and characterizing splits internal to a wooden member, that is also robust against the harsh environment of a typical lumber operation or the like and that is safer, less costly and more compact than instruments based on x-rays or other electromagnetic radiation.
The present inventors have discovered that splits create an acoustic discontinuity that may be detected by an ultrasonic signal transmitted through the wooden member across the grain at a number of different angles around the perimeter of the wooden member and comparing the received waveforms. Even after the splits have closed and are no longer visible, they create an acoustic discontinuity that may be detected. Detection of the splits may be used to control the operation of a saw to change cut locations or to modify the sawing technique.
Specifically, the present invention provides an apparatus for detecting splits in wooden members using at least one pair of opposed ultrasonic transducers positioned to contact the wooden members on opposed points along an axis across a grain of the wooden member. Driving circuitry drives one of the ultrasonic transducers so as to produce an ultrasonic wave of known characteristics and detection circuitry connected to an other of the ultrasonic transducers receives the ultrasonic wave after passage through the wooden member to provide a measurement. The wooden member measurement is repeated along axes at a plurality of angles about the outer perimeter of the wooden member across the grain of the wooden members, and an electronic computer communicating with the driving and detection circuits executes a stored program to compare the wooden member measurements at the plurality of angles to detect a split in the wooden member indicated by variation in the measurements.
Thus it is one object of the invention to provide a simple and inexpensive method of detecting splits in wooden members.
Multiple pairs of ultrasonic transducers may be each positioned to transmit and receive an ultrasonic wave along different circumferential angles or may use a movable carriage holding at least one pair of ultrasonic transducers and movable about the wooden member to position the ultrasonic transducers at the plurality of angles.
Thus it is another object of the invention to permit flexibility in selecting between electrical scanning employing multiple transducers or mechanical scanning employing a single or limited number of pairs of transducers.
The comparison performed by the apparatus may address the attenuation of total energy in the received ultrasonic wave, the change in spectral energy distribution in the received ultrasonic wave, the spreading of the temporal distribution of energy in the received ultrasonic wave, phase distortion in the received ultrasonic wave or combinations of the above.
Thus it is another object of the invention to provide for a multiparameter measurement so as to improve the accuracy and robustness of the ultrasonic measurements.
The apparatus may include a means for measuring the thickness of the wooden members along the axis and may calculate a time of flight of the ultrasonic wave between transducers to determine a sound velocity, or may determine a change in energy or phase as a function of thickness.
Thus it is another object of the invention to account for other factors affecting the received ultrasonic waveform so as to improve the ability of the apparatus to detect localized defects or other features within wooden members of varying thickness and type.
The apparatus may include a means for moving the wooden members with respect to the ultrasonic transducers perpendicular to the axis of the transducers and the output of the electronic computer may be a measure of wooden members"" quality as a function of position.
Thus it is another object of the invention to determine the length of splits for the purpose of guiding a cutting of the wooden member to optimize its usage.